March 



HARDWOOD RECORD 



17 



Some Wood Stains and Their Causes 



By Ernest E. Hubert 



Assistant Pathologist 



Bureau of Plant Industry in Co-operation with Forest Service 

 Forest Products Laboratory 



Most of the discoloratioiis or stains found in stored lumber or 

 wood products of various kinds arc caused by certain types of 

 organisms known as fungi. These minute plants secure their nour- 

 ishment from the wood they inhabit and as they develop they-find 

 means to progress from one wood cell to the other in order to reach 

 deeper into the wood in search of more food. As we learn more 

 about the wood staining fungi, we find new ones to add to the size- 

 able list, and we also find that the damage done is gi'eater than 

 formerly supposed. Blue stain or sap stain so common on pine 

 lumber and often found on hardwood lumber was estimated in 

 1911 to cause an annual loss of about eight and a quarter million 

 dollars.' 



Eecent investigations 

 made in co-operation 



with the Forest Prod- " 



uets Laboratory have 

 disclosed the fact that 

 fungi are responsible for 

 a large number of detri- 

 mental and disfiguring 

 stains in wood. Some 

 of the worst offenders 

 are found staining a va- 

 riety of hardwood prod- 

 ucts, such as barrel 

 staves, shovel, pick and 

 hammer handles, veneer, 

 furniture stock, wagon 

 and automobile stock, 

 airplane propeller 

 blanks, and lumber of 

 all descriptions. 



A few of the most im- 

 portant stains causing 

 loss through degrade 

 and cull are here pre- 

 sented with a brief dis- 

 cussion of methods of 

 control. 



The Grayish-Olive Stain 

 of Hardwoods 



Fig. 1. At A and D the fungus threads of the olive black mold arc seen penetrating the cell 



walls of persimmon wood. At B and C arc shown the spores and the crater-like fruiting bodies 



of the above fungus. Enlarged about 500 times 



This stain was first described by Humphreys " as common on stored 

 railroad tics cut from beech, red gum and persimmon. It has also 

 been found in black gum pulp logs kept in storage for experimental 

 use. The stain produced in wood by this fungus, Lasiosphaeria 

 pezizula, (Fig. 1), resembles somewhat the blue-stain in sapwood 

 caused by Ceratostomella sp., and to be discussed later, but differs 

 in that it is grayish olive in color instead of grayish blue. It stains 

 both heartwood and sapwood and is usually found penetrating the 

 cut ends from one to four inches. As in the case of blue-stain, the 

 presence of the fungus in the wood tissues imparts the "stain" 

 color to the wood. The fungus, in the form of minute threads 



' Weiss, H. F., and Barnum, C. T. The Prevention of .SVjfi Stain in lumber. 

 U. S. Dept. Agriculture Forest Service Circular 192: 1-19, 1911. 



- Humphrey, C. J. The decay of tics in storage. Proceed. American 

 Wood-Preseriers' Assoc. 16:217-250. PI. l-S. 1920. 



^ Kress, O., Humphrey, C. J., Richards, C. A., Brinj, M. W., and Staidl, 

 J. A. Deterioration nf Wood Pulp and Pulp Wood by Fungi and Methods 

 of Control. American Paper and Pulp Association, 1922. 



called hyphae, grows in length, branches and penetrates the cell 

 walls or the thin places in the walls. In this manner the stained 

 area is extended and the stain spreads. This mold-like plant 

 rarely penetrates the cell wall of the wood as in Fig. ID, but 

 searches out the natural openings and passes through these 

 (Fig. lA). 



This stain usually appears on stored material improperly piled 

 and exposed to the elements. 



The Yellow Stain of Birch, Hickory, Oak and Other Hardwoods 

 If you should find a "yellow streak" in your hardwood product 

 you can be reasonably certain that it is due to some fungus which 

 crept in when you "weren't lookin'." 



This very inconspicu- 

 ous yet troublesome yel- 

 low stain is often found 

 in the products manufac- 

 tured from some of the 

 well known hardwoods. 

 The stain develops in 

 the wood during the pe- 

 riod following the cut- 

 ting of the tree and be- 

 fore the wood is worked 

 up into the finished 

 product. Improper stor- 

 age of logs, lumber or 

 stock of any kind under 

 conditions favorable for 

 fungous growth may 

 cause this stain to de- 

 velop. A moldy appear- 

 ance of the stock may 

 be the first symptom. 

 It has been observed 

 in birch veneer, birch 

 used in airplane manu- 

 facture, hickory and 

 maple handles for va- 

 rious implements, such 

 as shovels, hoes, ham- 

 mers and axes, in oak 

 laminations used in air- 

 plane propellers, in oak wagon felloes and spokes and in oak lumber. 

 The stain is of a pale yellow color, usually in streaks or irregular 

 spots, and is most easily detected when the wood is surfaced. The 

 fungus is also found in areas of the wood, showing very faint to 

 no discoloration. Hy cutting thin sections of the yellowed wood 

 and examining under the microscope numerous minute colorless 

 fungous threads are found winding their way within the wood cells, 

 occasionally penetrating the cell walls. Upon making artificial cul- 

 tures of this yellow wood a fungus is produced which is mold-like in 

 character, olive buff in color and which grows rapidly under proper 

 moisture conditions. It is classed in the Penicillium divari- 

 catum group, and resembles somewhat the fungus which is found 

 on stored wood pulp." 



The principal loss due to this stain is in the discoloration of the 

 finished product. The stain often runs deep into the wood and can 

 not be surfaced off. The purchaser is continually on the lookout 

 for imperfections in axe and other tool handles which to him may 



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